1. Field of the Invention
Embodiments of the present invention relate generally to transistor aging and, more specifically, to estimating and monitoring the effects of transistor aging.
2. Description of the Related Art
Circuits that include transistors experience aging effects. Aging causes the performance of transistors in the circuits to degrade. More specifically, the switching speed of the transistor increases when the transistor ages. Adjusting for the effects of aging is typically difficult, as there may be millions of transistors in a circuit. Further, due to the physical size of the transistors, transistors within circuits may be difficult to probe or modify in an attempt to compensate for aging effects.
Some techniques for monitoring and adjusting for the effects of transistor aging have been developed. In one such technique, the overall aging of a circuit during the lifetime of the circuit may be estimated at manufacturing time, or at some other early time, and the different elements of the circuit may be “margined” according to that estimate. When so margined, the circuit is operated using parameters that are based on the characteristics of an aged version of the circuit. For example, a “margined” circuit would always be operated within clock frequency and power supply voltage ranges that are based on the end of life characteristics of the circuit, regardless of whether the circuit is one day old or 3 years old.
However, when a circuit is new, the circuit has the capability to operate within power supply voltage ranges that cause the circuit to consume less power and/or to operate faster than when the circuit is aged. Consequently, operating a margined circuit requires an increase in power supply voltage. Alternatively, if a higher power supply voltage is not provided, then the circuit operates at a lower clock frequency, which causes the speed of operation of the circuit to decrease.
As the foregoing illustrates, what is needed in the art is a technique for adaptively monitoring and/or adjusting for the effects of transistor aging in circuits.